While eating in Tang Palace, I carry 3 of my wide angle lenses, which were attached to Sony A7 body.

The lenses were Zeiss 18mm, Sigma 15mm and Sony's own 28mm F2.

This three wide lenses were favorite among Sony and Canon users.

Do note that this three lenses are actually pretty different, one is an Ultra Wide Angle lens, the other is Fish Eye and the last is Wide Angle lens. So this comparison isn't going to ponder on the details like sharpness and micro contrast etc.

Taking the review from DXO Mark is quite apparent that Sony 28mm is technically better than the zeiss 18mm, but the 18mm being an Ultra Wide Angle lens have a more interesting result and more pleasing for me.

The Sigma 15mm is a fish eye lens, it has a whimsical look that would be great for some subjects, but on this particular interior shot, the curvature is a bit distracting. I would usually use the adaptive wide angle feature on photoshop and crop some top and bottom part of the image to lessen the distortion , such as what I did in the photo below taken inCitrus Lee

You can draw your own conclusion from the photos above. Preferences would be greatly affected by taste, since the focal length difference in wide angle lenses are huge, in comparison to tele lens, such as this macro lens comparison here Sony vs Canon Macro Lens.

My conclusion after comparing this 3 lenses result, the overall winner is the sony 28mm which produce clean image and good sharpness. But the zeiss 18mm ends up being my favorite lens, since they produce a very interesting image.

For my own preference, which is of course subjective, is like this : Zeiss 18mm -> Sony 28mm -> Sigma 15mm.

Sigma itself produce one of the sharpest image, but the distortion and strange field of view means there are challenges in using it as everyday lens.